Method and apparatus for gear checking



Feb. 13, 1945.

L.. D. MARTIN 2,369,477

METHOD AND APPARATUS FOR GEAR CHECKING Filed Mar ch 4, 1943 5 Sheets-Sheet 1 lnTln FIG. I.

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Patented Feb. 13, 1945 1 METHODAND APPARATUS FOR GEAR a CHECKING Louis D. Martin, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y.,]a corporation of New Jersey Application March4, letaserismaivaon 14 Claims. (01. 33-1795) This inventionrelates to gear checking machines. One object of my invention is to provide a machine in which a master tool, a rack-like instrument which is actually not a truerack, is used to check a gear by moving the master tool teeth into contact with the gear teeth. Another object of my invention is to" provide a checking machine having a higher degree of accuracy than known types of checking or gauging machines. Another object is to provide a machine which can be quickly set up and in which gears can be checked with considerable rapidity. Another object is to provide a machine for checking a large variety of gears from a single master tool and other objects will appear from the following specification, the novel features beingparticularly pointed out in the claims at the end thereof.

It has been customary to check gears by meshing and running them with master gears, measuring the distance between centers of the gears and noting the variations from the theoretically per.-

Such machines, however, cannot have a degree of accuracy exceeding that of the master gear used. Master gear eccentricity can seldom be held closer than .0005" to a desired dimension be relatively long, as for instance ten or twelve inches, the transverse curvature of the teeth may amount to only a fewthousandths of an inch.

and toothspacing and approximate shape can seldom be held closer than .0002". T This, then, is

an indication of the maximum accuracy that can be measured. The reason for this is that gear forming machines, including theindexing of the gears, for grinding or milling teeth are not capable of more accurate work.

I have overcome the difficultyof havingthe accuracy of checking depend on the accuracy of a'master gear by not utilizing such a gear. I have found that a worm section has so many advantages over a master gear that a farmers efiicient machine can be built utilizing such a testing tool.

A master wormsection difiers from a rack in that the former is in effect a section of a single spiral tooth so that the shaping and spacing of r the small sectionsof the tooth used as successive teeth in the master worm can be ground to a dimension at least "ten times asaccurate as a master gear or master rack. v

. Such a worm section may superficially resemble a rack but it difiers materially. The worm-section teeth have botha transverse curvature and a lead, andpreferably the radii of curvature may be long and thelead angle slight so thatoften to the eye the worm section appears much the same as a rack. As the worm sectionused maybe only a few degrees orso of the 360 of a full worm, and'as a convenient pitch diameter may machine shown in Fig. 6 but These dimensions are only to visualize a single typical example. Theworm-sections may be of any. required dimension.

Such worm-sections will be the mate or conjugate of all gears of the particular gearsystem used. 'The involutecurve is almost universally used today, and for this reason it is preferred; but :theform may be cycloidal, epicycloid, involute or any other desired tooth form.

Coming now to the drawingswherein like reference characters denote. like parts throughout: .Fig. 1 is a top planview of a gear checking machineiconstructed in accordance and embodying a preferredform of my invention;

Fig. 2 is a section taken on line 2-2 of Fig. 1; Fig. 3 is a fragmentary detail section taken on line 13'-3 of Fig. 2;

Fig. 4 is afragmentary detail section taken on line 4--4 of Fig. 2;

i Fig. 5 is a fragmentary detail section taken on line 5--5 of Fig.' 2 but with the parts in a different position; Fig.. 6 is afragmentary sectiontaken on line .6-6 of Fig. 1 part'sbeing broken away for the sake of clearness; i i

Fig. 7 is a front elevation of a portion of the with certain parts in a different position; i

Fig. 8 is an enlarged fragmentary detail section showing the relation of the worm section and slideway with parts'being omitted;

Fig. 9 is an enlarged perspective of a portion of a gear to be tested and a worm section, certain parts being shown on a much exaggerated scale;

Fig. 10 is a fragmentary sectional detail of a typical worm sectionand gear in testing relationship; and

i Fig. .11 is a view similar to Fig. 10 but with a somewhat different embodiment of myinvention. 1

My invention broadly comprises a machine on which a testing tool,which is a rack-like member,

is used toutest a gear by mating the rack-like member and a gear and moving one relative to the other until one complete revolution is made noting minute variations'in the. movement of the gear to and from the testing tool on an indicator. .Thus, eccentricity, uniformity ofteeth andlpitch diameter can belreadily checked and, if necessary, the imperfections can be noted on the gear if desired. My .machinealso. provides a simple means for determining with; extreme accuracy whether or not the pitch diameter of the gear is accurate.

Since the testing tool is an important part of the gear checking machine, it will be described first and for the more complete description of it reference may be had to my copending application entitled, Gear testing tool,? Serial No. 478,043, filed March 4, 1943, resulting in Patent No. 2,350,788, granted June 6, 1944. 'As indicated in this application the gear testin tool designated herein broadly as T may consist, as best shown in Fig. 9, of a bar of metal! which may have inclined walls 2 making the bar roughly V- shaped in cross-section. It may have a fiat lower wall 3 which is provided with a notch 4' (:Fig. 8')

to engage a pin 5 for moving the rack-like mem.- ber as will be hereinafter more fully described.

It should be noted that this coupling, the notch.

provided-with a T-slot M for the reception of a locking nut l5 having a handle l6 operable over a screw I! for looking a slide IS on the table or slideway l3. The slide 18 may revolubly support a post l9 carrying a worm gear 26, which, asbest shown in Fig. 5, meshes with a worm 2| which may be turned, by the knurled wheel 22. Thus the post may be. rotated and, in addition, it may be held in a set' position by a screw 23 passing through the pinch lugs 24.

It is customary to set the slide HS in the desired position to" cause the work gear W to be in position to mesh with the worm rack T.

The post I9 also carries a head 25 which may be. raised. and lowered on the post I9 by means of a. rack 26. withwhich a gear 27 meshes. Gear 4 and pin 5, is a loose one and the pin is short of the bottom of the notch 4. This is' to cause the worm section rails! to always lie firmly on the rail II as there can be no tendency for the. pin5 toraise the Wormsection from its slideway.

The rack-like member is provided with teeth. 6"

can be made with a degree of accuracy which is impossible in making the teeth of a true rack. A rack M, as also indicated in Fig. 9,. has teeth. N which must be milledor groundso that the accuracy of such teeth must depend in part upon the accuracy ofian indexing; machine which may move the member M each time a tooth is'milled or ground. Such teeth can seldom beheld closer than plus or minus approximately two ten thousandths of aninch. However, the worm section T has'a far greater degree of accuracy in both the spacingand shape of the teeth 6 because these teeth may be ground as a helix on a ma chine in which the grinding wheel is advanced with an exceedingly accurate, movement. It is believed that the teeth spacing and accurate shape of the teeth is of course largely due to the fact that actually the teeth 6 are in effect cut from one long tooth which; can be accurately made because the machines for, advancing the tooth grinding wheel are capable of. producing exceedingly accurate leads and tooth form.

In other words the worm section T is much.

like a hob without relief. A worm section is the mate or conjugate of all thegears of the tooth system used for the worm section and. this is true regardless of the tooth form system used in the worm section. Thus the teeth may be of the usual involute. type, which is by far the most universally used today,.or the tooth shape may be cycloidal, epicycloid or any other known type of tooth shape;

It is possible to test any kind of gear having the same tooth system whether the gear'has; teeth parallel to the gear axis or at an angle thereto as will be more fully described.

The drawings illustrate a preferred embodiment of my machine which may consist of a base member l0 including a pair of V-shaped rails ll extending along the front of the base to slidably support the gear testing tool T. From the front i2 of the base, a fiat table-like portion l3. may extendrearwardly. this. portion ofv the base bein 27 is carried by a shaft 28 and may be operated by the. knurled Wheel 29. Referring to Fig. 4 the post l9. may be locked in any set position by a hand wheel 30 which may be turned tooperate the screw- 34,. thus drawing the locking bar 32 intolocking engagement with the post. wthereby holding the head25 inits set position. The head. 25 constitutes a portion of the work holder. The work. gear W may be mounted on a shaft 33 which can conveniently have a tapered portion 34 mating-with a. tapered aperture 35 andv this shaft may beheld in place by a thumb screw 36 having a threaded engagement at 3'! with. the shaft 35. Set screws 38 by entering a groove 39- in the nut 36 hold the shaft with extreme accuracy in its proper, position in which itmay move toand from the gear testin tool T in the tollowing'manner. 1

The shaft. 34 iscarried by-a plunger 40. mounted to slide in bearings 4i and 42 in the'head: 2-5. The extent, ofv movement may be controlled by a pin 43 entering a. notch 44-, this pin being movable to and from. the. notch by means of a hand wheel 4-5. Av pair of pins 46, best shown in Fig. 3, adjustable by the screws 41 which are covered by cap screws 48,, accurately guide the plunger by entering the. grooves 40. therein. An anvil'49 extends upwardly through. the top or cap and into a. position in which: it may be engaged by the. plunger 5| of an indicator 52 of the type in-,

eluding a movable ring 53- extending around. the

outside: of. the. indicator so that thev arrow 54 may be set back to a zero position. as shown in Fig. 6

through movement of thering 53.

Thus, if the work gear W is meshed with the testing tool T, as in Fig. 6, and the testing tool which isa worm. section is moved back or forth by meansof a knob 55, a shaft 56, a gear "51 anda tic'ed that a high degree of accuracy of measurement can: be made because the testing tool Tin Fig.9,- T and T in- Figs. .10 and. 11, all include teeth 6 havin lateral curvature. This lateral curvatureis, exaggerated in these drawings to more clearly bring out the fact that therewill bezonly contact in. a single plane: A (Figs. 10 and 11) through the work gear W and W andthe worm section. T and T. This is an advantage because. by; moving the: work\ aears.-.transverse1v than the tool T of the axis A the contour of anylportion ofthe teeth throughout their length can be readily tested. i i

Figs. 1 and 9 illustrate a typical arrangement gears are largely a matter of selection and not highly important. i

Returning to Fig. 2, it will be noticed that the plunger 40 carried by the head 25 also carries a transversearm which contacts a plunger 62 pressed upwardly by a spring 63 and adjustable u by a screw 84. I prefer to adjust this spring so that it slightly under counterbalances the weight forthwith the work gear Wmeshing with the gear testing tool or worm section T. the lowest position as shownby the indicator 52 will necessarily indicate that the teeth of the work gear W are in angular alignment with the tool T. By then measuring the distance betweenthe posts H and 12 the angle a may be determined I by measuring chord of the subtended arc. Thus 9 it is asimple matter to determine the actual lead angle of teeth.

In order to prevent dust or dirt from getting between they -shaped rails I I on the base If), and i between the corresponding V-shaped rails 2 on the worm section, I prefer to -provide a cover plate 80 having downwardly extendingflanges 8| and having an aperture 82 of a size to receivethe upwardly projecting portion 83 ,of the worm section as bestshown in Fig. 8. An aperturestrip of theplunger 4|],the shaft 34 and the Work gear W, so that the work gear W will rest against the worm section -T with a light pressure but can easily be raised therefrom either manually or in minute amounts due to gear. l

The indicator 52 may conveniently be carried by a shaft 65 adjustable by a screw 66 in a hearing 61 so that the initial setup of the indicator can be easily and accurately made.

Figs. 1 and 2, as well as Fig. 4, show my testing machine setup for testing gears with teeth parallel to the axis-of the gear. However, a worm section T as above explained is suitable for testing any other gears having the same tooth system of the same pitch-size, and if it should'be desired to test a work gear W inwhich the teeth 10 are not parallel to the. axis of the gear, the tester may be readily setup as indicated in Fig. 5 by turning the post l9 so that the head will turn-through the required angle.

In order to determine the required angle I haveprovided a pair of pins H mounted on the head 25 and 72 mounted on the slide l8. These pins are ofknown diameter-say one-half inch and each pin is provided with a half flat end '13 and 14; these flats being accurately faced. The

pins '1! and 12 are held in place by set screws '15 and it and when the flats "l3 and I4 lie smoothly in contact the axis of the shaft 34 is at'right angles to the slideways II and when the pins are separated this angle varies.

Since the centers of the pins H and i2 relative to the center of the post I9-that is the distance D1is" known, it is a simple matter to set the head 25 for any. required gear lead angle by figuring. out the chord of the subtended angle and by using amicrometer TI to measure the angled between the centers of the two pins as indicated in Fig. 5.

work piece W being tested is correct. If the im- 'strument should be set for a lead angle of, say,,

and the gear should have been imperfectly imperfections in the work 84 may be employed to raisethe cover 810. to avoid contact with the rails l I if the shape of the worm I section requires it.

It should be noticed that the tool in Gig. 6) p Thisincludes a pad 90 on the end of this tool. pad bears a definite relationshipto the pitch line ofthe wormsection vT andto the pitch diameter of the work gear -W and preferably the pad 98 x forms a'gauge blockexactly on the pitch line. i The reason for this is that by sliding the tool T until the pad 96 lies beneath a shaft of known diameter which may support the work gear W, this pad may be used with suitable test blocks, such as Johansson test blocks, to determine accurately the center position of a work gear. For .mostpurposes the most convenient way to obtain the pitch diameter of a gear is to usetthis pad 90 with a test block, but I alsoprovide a second means for determining this by means of a builtin micrometer 9f, the plunger of which 92 is carried in a bracket93 and the anvil 91 of which is carried by. a bracket. 95 and may be positioned by a set screw 96. The adjustable bracket 95 maybe mounted to slide upon the post l9 and may be locked in a set position by means of the knob 97",. the notched shaft 91 and the screw 98. By turning the. knob 96 the curved notch pinches the shaft 19 holding the bracket in a set position.

A micrometer 9! may be used in setting up the machine in the following manner.

The pitch line pad .90 of thegear testing tool maybe moved in alignment with the shaft .33 an'd the head 25 may be lowereduntil the shaft rests upon the pad 90. The diameter of the shaft 33 cut, by oscillatingthehead25 slightly back and is known and if it is desirable to accurately raise the shaft any distance, such as for instance ,lfthe nut 56 is released and the anvil 94 is brought into contact with the plunger 92 at a known read ing, as for instance a zero reading. The head 25 is then raised and by turning down the plunger 92 the required 1'', for instance, and bringing it into contact with the anvil 94; the exact. distance between the shaft 33 and the pad is. knowni -i It is usually desirable to move the worm section T a distance necessary to. turn the work gear W through 360 in order to test all of the teeth on the gear and I provide a pair of stops in'g helical gears as well".-

and m of. the rack driving the worm. section. when ithas been moved: a distance. sutficientto rotate the gear W exactly one revolution.

It should be especially noticed-I that my. ma-

chine-is adapted for testing not only simple spur machine in addition to its primary function of testing the usual types ofgearsand production testing. I I v I have shown an indicator 52 mounted directly upon my instrument, but if desired an indicating measuring device may be placed separated from-the machine and may be electrically connected thereto. A suitable device is on the market, being known as an Electro limit gauge, supplied by Pratt 8t Whitney. This comes with a very large dial graduated into units of one tenthousandth of an inch and is very easy to-attach and use. r

While I have described and illustrated a preferred embodiment of my gear checking machine in whicha rack-like tool, which is actually a worm section, isused as the master member, it is obvious that .various' oth'er embodiments can be devised which come within the scope of the appended claims. I

What I claim is:

1. In a gear checking machine, the combination with a. base, of a slideway thereon, a worm section rack mounted to slide in the slideway,

means for moving the worm section rack carried by the base, a bracket for revolubly carrying a gear to betested with the teeth thereof meshing with worm section rack; said bracket comprising a slide movably mounted on the base, a vertical post carried by the slide, and meansfor turning the post about! its own axis.

slide, a head sl-idably' mounted on the post, said head including a: gear supporting shaft, and a plurger carrying the gear supporting shaft slidably mounted on the head.

3-; In a gear checking machine, the combination I with a base, of a slideway thereon, a worm section mounted to slide in the slideway, means'for moving: the worm section rack carried by'the base, abracket' for revolubly-carrying a gear to be tested with the teeth thereof meshing with worm- 'a. plunger carrying the gear supporting shaft slidably mounted. on. the head, a counterbalance connected to the plunger of .insufficient strength in its smarte -cw a we Wit y said. plunger may normally meslzr withv said worm section. l

4. In a gear checking machine, the combination withabase, ofv a slideway thereon, a worm section mounted to. slide in the slideway, means for mov;- ing. the worm section carried by the base, a bracket for revolubly carrying a gear to be tested with the teeth thereof. meshing with. worm section rack, said bracket comprising a slide movably mounted on the base, a vertical post carried by theslide, ahead slidably mounted on the post,

. said head. including a gear supporting shaft, and

a plunger carrying the. gear supporting. shaft slidabl-y mounted on the head, and a micrometer anvil also carried by the: plunger, a micrometer mounted directly above the anvil and contacting therewith to measure movements of said plunger.

5. In a gear checking machine, the. combina tion with a base, of a slideway thereon, a worm section mounted to slide in the slideway, means for moving the worm section carriedv by the base,

a bracket for revolubly carrying, a. gear to be tested with the teeth thereof meshing, with worm sectionrack, said. bracket comprising a slide movably mounted onthe base, a vertical post carried by the slide, a, head. movably mounted on said post, means for changing the angular relation between the head and slide and means for defining the. angular relation comprising a pair of round pins equally spaced from the. post.

r 6. In a gear'checking machine, the combination with a base, of. a slideway thereon, a worm section mounted to slide in the slideway, means for moving. the worm section carried by the. base, a bracket for revolubly carrying a. gear to be tested with the teeth thereof. meshing with worm sec- .tion, said bracket comprising a. slide movably section'mounted. in the slideway, means on the base for moving the worm section, means carried by the base for. resiliently supporting a gear to be tested with the teeth thereof in mesh with the teeth of the wormv section, and. a test. block carried by the worm section and including, a means for determining. the .pitchdiameter of the gear therefrom.

I 8. In a gear checking machine, the combination with a base, a slideway thereon, a worm section mounted in the slideway, means on the base for moving the worm section, means carried by the base for resiliently supportinga gear to be tested with the. teeth therefrom. in mesh with the teeth of the worm section, and a slideway cover closely fitting the worm section and movable therewith to exclude foreign matter therefronm. r

9. In a gear checking machine, the combination with a base, a slideway thereon, a worm section mounted in the slideway, means on the .base for moving the worm section, means carried by the base for resiliently supporting a gearto be tested with the. teeth thereof in mesh with the teeth of the worm section, and adjustable stop members carried by the slideway for. limit ing movement or thewormsection,

10. In a gear checking machine, the combination with a base, a slid'eiway thereon, a worm section mounted in the slideway, means on the base for moving the wormi-section, means carried by the base for resiliently supporting a gear to be tested with the teeth thereof in mesh with the teeth of the worm section, said means for moving the worm section on the baseincluding a rack and Pinion. I

11. In a gear checking machine, the combination with a base, a slideway thereon, a worm section mounted in the slideway, means on the base for moving the worm section, means carried by the base for resiliently supporting a gear to be tested with the teeth thereof in mesh with the teeth of the worm section, said means for moving the worm section on the base including a rack and pinion and a coupling between the worm section and the rack and pinion for transmitting motion.

ting the worm section and adapted to be moved thereby.

13. In a gear checking machine, the combination with a base, a slideway thereon, a worm section mounted in the slideway, means on the base for moving the worm section, means carried by the base for moving the worm section, means carried by the base for resiliently supporting a gear to be tested with the teeth thereof in mesh with the teeth of the worm section, a cover extending over the slideway, said cover including an aperture closely fitting the worm section and adapted to be moved thereby, said cover being supported solely by the worm section and extending therefrom into a slideway protecting position.

14. In a gear checking machine, the combination with a base, a slideway thereon, a worm sec- 12. In a gear checking machine, the combina-I tion with a base, a slideway thereon, a worm section mounted on the slideway, means on the base I for moving the worm section, means carried by the base for resiliently supporting a gearto be tested with the teeth thereof, in mesh with the teeth of the worm section, a cover for the slideway, said coverincluding an aperture closely nttion mounted in the slideway, means on the base worm in its slideway and the worm whereby the worm may always lie firmly on and be supported solely by the slideway.

LOUIS D. MARTIN. 

